Method and apparatus for consolidating soils and improving the base bearing for foundation structures

ABSTRACT

A method for consolidating soils and foundation structures. Under the zone to be consolidated, a hollow impermeable rigid wall pressure cell or chamber is inserted, this cell communicating with the outside by means of an injection conduit and a vent conduit, then over said chamber or cell erecting the foundation structures (piles, walls, etc.), next injecting through the injection conduit a pressure binder mixture within the chamber previously introduced into the soil, then closing the vent conduit and continuing to inject pressure binder mixture until destroying the impermeability of said chamber and enabling a tamping or stuffing up of the neighbouring soil, then closing also the injection conduit and maintaining it at closed condition until the binder mixter injected into the soil has set, and finally washing or scavenging in site the pressure cell, whereupon the injection operation of the pressure binder mixture into the cell can be repeated also for many times by following the same method and through the same device above described.

United States Patent Chitis METHOD AND APPARATUS FOR CONSOLIDATING SOILSAND IMPROVING THE BASE BEARING FOR FOUNDATION STRUCTURES Wolf Chitis,Corso Vittorio Emanuele 167/0, Napoli, Italy Filed: Apr. I9, I972 Appl.No.1 245,568

Inventor:

Foreign Application Priority Data Nov. 8, 1971 Italy 40441 A/7l Dec. 3,1971 Italy 40445 A/71 References Cited UNITED STATES PATENTS Turzillo61/35 Primary Examiner.Mervin Stein Assistant ExaminerAlex Grosz [5 7ABSTRACT A method for consolidating soils and foundation structures.Under the zone to be consolidated, a hollow impermeable rigid wallpressure cell or chamber is inserted, this cell communicating with theoutside by means of an injection conduit and a vent conduit, then oversaid chamber or cell erecting the foundation structures (piles, walls,etc.), next injecting through the injection conduit a pressure bindermixture within the chamber previously introduced into the soil, thenclosing the vent conduit and continuing to inject pressure bindermixture until destroying the impermeability of said chamber and enablinga tamping or stuffing up of the neighbouring soil, then closing also theinjection conduit and maintaining it at closed condition until thebinder mixter injected into the soil has set, and finally washing orscavenging in site the pressure cell, whereupon the injection operationof the pressure binder mixture into the cell can be repeated also formany times by following the same method and through the same deviceabove described.

7 Claims, 2 Drawing Figures METHOD AND APPARATUS FOR CONSOLTDATTNG SOILSAND IMPROVING THE BASE BEARING FOR FOUNDATION STRUCTURES Site castconcrete piles are known, the load bearing capability of which isgenerally committed to the side friction soil resistance against thepile surface and base resistance on the soil bearing. Either woulddepend on the mechanical characteristics of the soil, as naturally such.

Evidently, where this base soil should be subjected to precompression,such as to increase the consistency thereof, the pile usable loadbearing capability would be increased. A similar effect could beprovided, where possible, by grouting the soil adjacent the pile base orfoot.

Therefore, the device according to the present invention aims to provideat the base of a pile or similar structure, as site cast, a distributedpressure and pile base soil tamping and, subordinately, a soil grouting,such that a strain is exerted both against the pile base (or similarstructure) and neighbouring soil. The device eseentially comprises ahollow impermeable resistant shell (pressure cell) which is introducedinto the soil prior to casting and arranged at the pile base. The shellwall is made watertight and impermeable to prevent the internal cavityfrom being filled with cement liquid as the pile or similar structure iscast.

Upon cast completion, said shell is pressurized by injecting therein abinding mixture (either ofa cement or chemical type), that is capable ofsetting and hardening after some time.

Among its features, the device according to the invention ischaracterized in that the impermeable shell wall, or even the shellalone, will break up as a result of the expansion caused by the bindingmixture pres sure, thus allowing the pressure liquid to diffuse withinthe soil and impregnate the same. Thus, the soil grouting effect willadd to the mechanical tamping effect.

A possible device, such as described, is diagrammatically shown in theaccompanying drawing in which:

FIG. 1 is a vertical section of the device; and

FIG. 2 is a plan view of the device.

The inventive device comprises two plates and 10' facing each other soas to provide an inner space lll which is maintained by spacing means12. An injection conduit 13 terminates in said cavity 11 and a ventconduit 14 branches therefrom. The device walls or plates 10, 10 areprovided with a set of through holes 15 and the whole device body isenclosed by an impermeable shell 16. For example, this shell cancomprise one or more layers ofjute cloth or the like, externally coatedwith an impermeable plastic sheet. This serves the purpose offacilitating through the cloth thickness the ejection of water formingthe injection binder mixture, whereby the latter may exhibit a higherdensity and strength.

The device is placed on the soil at the cast base or foot (pile, wall,etc.) whereupon the casting for said overhanging structure (pile, wall,etc.) is effected. When the overhanging cement casting has set andconsolidated, the device cavity (which has remained free ofcontamination owing to the impermeable shell 16) is filled with bindingmixtures through the injection hole 13. Air exits from the vent tube 14.Then, by closing said vent tube 14 and pressurizing the injected liquid,the latter will cause the whole assembly to expand,

that is plates 10, 10' will separate, the impermeable shell 16 will befilled with pressure liquid and break up at a plurality of locations,particularly towards the soil, and the liquid binding mixture will exit,thus impregnating and tamping the soil. When deeming that a convenientoperation stage has been attained, for example when the soil hasabsorbed a sufficient amount of cement binder for its consolidation, theinjection of binding mixture is shut off,'the injection tube 13 istightly sealed and maintained at a constant pressure, such as by meansof a gate or other system, until said pressure liquid has set.whereupon, washing or scavenging can be effected for the whole assemblycomprising the cell and the two injection and vent tubes, so that asecond injection operation at a higher pressure can be repeated.

The device pressurization can be repeated also for many times atindefinite intervals. For example and particularly in loose soils, sucha repetition would enable to recover or balance any sinkings a pilemight undergo in time.

1 The use of the above device will allow to experimentally obtain thevalues of the side friction strength for a pile. Thus, by graduallyloading the base cell 10, 10', the diagram can be obtained for the pilestresses of raising, similarly as an ordinary loading test. Thus, theaverage side strength for side friction against the pile can beobtained.

2. By inserting along the pile trunk suitable commercially availableinstruments, it is also possible to obtain through the concrete stresscondition the various side strength values at the various levels;therefore, instead of the average value of side friction, the value canbe obtained as corresponding to the various layers. In any case, bysuitably increasing the pressure within the base cell 10, 10' tosufficiently high values, the total load limit rate, by side friction,for the entire pile can be obtained.

3. Where the pile is of a sufficient length, or sufficiently bounded atthe top or head end, the soil strength values for base load bearing canbe obtained, and in the case the limit load still for base load bearing,beyond which the soil would collapse.

4. As stated at points (2) and (3), by means of the pressure cell 10, 10it is thus possible to effect an actual pile loading test, from whichsuch interest values can be obtained as useful load, limit load,sinkings, etc.

5. Should the pile be provided along its trunk with the instruments asmentioned at point (2), the good provision and continuity for thecasting can be controlled. Thus, when pressurizing cell 1t), 10 andshould, for example, the pile be interrupted at a section, suchinstruments would detect stress values only at the trunk below theinterruption, while above the interruption the values would be reducedor be zero depending on the discontinuity magnitude. It should bepointed out that at the loading tests mentioned above, the pressure cell10, 10' substantially acts as a jack.

However, the invention importance essentially resides in a substantialunlimited cell expansion, when the stroke of an ordinary jack isnecessarily limited.

It should be also specified that the sinking of a pile which has beenpreviously pressurized through the base cell M), 10' according to thepresent invention will be at any rate lower than that of an ordinarypile, and this due to both soil tamping and soil chamber laterally ofthe pile trunk.

6. A further application of the pressure cell 10, is to be found in theinjection field. By inserting a cell of the above type into an injectionhole of a convenient diameter, and by tamping at the top, repeatedinjections can be carried out, which in addition to mixture diffusing,also attain the purpose of soil tamping.

What 1 claim is:

1. A method for consolidating soil and improving the bearing base for afoundation structure, comprising the steps of (a) introducing beneaththe soil surface a ho]- low enclosed cell member having an injectionconduit member and a vent conduit member establishing communicationbetween the interior of said cell member and the atmosphere above thesoil surface and said cell having an impermeable, rupturable coversurrounding it, (b) erecting a foundation member in a position abovesaid cell member, (c) injecting into said cell member through theinjection conduit member a binder mixture under increased pressuresufficient to rupture said impermeable covering and to cause said bindermixture to penetrate the soil neighboring said cell member, (d) whilemaintaining said increased pressure, causing said binder mixtureinjected into the soil to set, (e) injecting into said cell memberthrough the injection member a washing liquid thereby washing all unsetbinder mixture from the interior of said cell member and from saidinjection conduit and vent conduit members, and (f) repeating at leastonce the steps (c), (d) and (e) set forth above.

2. The method according to claim 1, further comprising the step ofproviding means responsive to said injection of binder mixture underpressure for measuring physical forces exerted on said foundationstructure by the soil as a result of'said injection of binder mixture.

3. The method according to claim 2, wherein said measuring means isincorporated in the foundation member.

4. The method according to claim 1, wherein said foundation member is aconcrete structure.

5. A device suitable for introduction into the soil to effectconsolidation thereof and improve the bearing support for foundationstructures, comprising a hollow enclosed cell member comprised of twoopposing apertured plates separated from one another and mutuallysupported by a plurality of spacing means, an injection conduit membercommunicating with the interior chamber of said cell, a vent conduitmember communicating with the interior chamber of said cell, and acovering layer surrounding said cell, said cover being impermeable butcapable of being ruptured by means of a binder mixture forced underpressure into the hollow interior of said cell through said injectionconduit member.

6. The device according to claim 5, wherein said cell comprises twoopposing apertured convex-concave plates separated from one another andmutually supported by a plurality of spacing means.

7. The device according to claim 5, wherein said covering comprises atleast one layer of jute linen and a second exterior layer of impermeableplastic material.

1. A method for consolidating soil and improving the bearing base for afoundation structure, comprising the steps of (a) introducing beneaththe soil surface a hollow enclosed cell member having an injectionconduit member and a vent conduit member establishing communicationbetween the interior of said cell member and the atmosphere above thesoil surface and said cell having an impermeable, rupturable coversurrounding it, (b) erecting a foundation member in a position abovesaid cell member, (c) injecting into said cell member through theinjection conduit member a binder mixture under increased pressuresufficient to rupture said impermeable covering and to cause said bindermixture to penetrate the soil neighboring said cell member, (d) whilemaintaining said increased pressure, causing said binder mixtureinjected into the soil to set, (e) injecting into said cell memberthrough the injection member a washing liquid thereby washing all unsetbinder mixture from the interior of said cell member and from saidinjection conduit and vent conduit members, and (f) repeating at leastonce the steps (c), (d) and (e) set forth above.
 2. The method accordingto claim 1, further comprising the step of providing means responsive tosaid injection of binder mixture under pressure for measuring physicalforces exerted on said foundation structure by the soil as a result ofsaid injection of binder mixture.
 3. The method according to claim 2,wherein said measuring means is incorporated in the foundation member.4. The method according to claim 1, wherein said foundation member is aconcrete structure.
 5. A device suitable for introduction into the soilto effect consolidation thereof and improve the bearing support forfoundation structures, comprising a hollow enclosed cell membercomprised of two opposing apertured plates separated from one anotherand mutually supported by a plurality of spacing means, an injectionconduit member communicating with the interior chamber of said cell, avent conduit member communicating with the interior chamber of saidcell, and a covering layer surrounding said cell, said cover beingimpermeable but capable of being ruptured by means of a binder mixtureforced under pressure into the hollow interior of said cell through saidinjection conduit member.
 6. The device according to claim 5, whereinsaid cell comprises two opposing apertured convex-concave platesseparated from one another and mutually supported by a plurality ofspacing means.
 7. The device according to claim 5, wherein said coveringcomprises at least one layer of jute linen and a second exterior layerof impermeable plastic material.